AboutZoos, Since 2008


Habi­tat frag­men­ta­tion affects gene flow in leop­ard and tiger populations

pub­lished 31 July 2013 | mod­i­fied 30 May 2014

As rapid eco­nomic expan­sion con­tin­ues to shape the Asian land­scape on which many species depend, time is run­ning out for con­ser­va­tion­ists aim­ing to save wildlife such as endan­gered tigers and leop­ards. Their habi­tats get frag­mented, but these big cats are still able to migrate via small cor­ri­dors of for­est and stay con­nected and genet­i­cally strong — until now, recent stud­ies revealed.

Bengal tiger cubsAs eco­nomic expan­sion and devel­op­ment frag­ments the for­est land­scape of cen­tral India, the species that rely on that habi­tat — includ­ing endan­gered tigers and leop­ards — face dwin­dling pop­u­la­tions and increased com­pe­ti­tion for food and resources. Smith­son­ian Con­ser­va­tion Biol­ogy Insti­tute (SCBI) sci­en­tists analysed the genes of these big cats in the Satpura-​Maikal land­scape — a 15,000 km2 area com­posed of four inter­con­nected reserves: Kanha, Sat­pura, Mel­ghat and Pench. From April-​June 2009 and Novem­ber 2009-​May 2010, they col­lected scat (fecal mat­ter) and hair sam­ples for DNA analy­sis. This data, com­bined with India’s for­est ecol­ogy his­tory, enabled SCBI sci­en­tists to con­struct a defin­i­tive pic­ture of how habi­tat loss affects the genetic diver­sity and gene flow of cat pop­u­la­tions. Pub­lished in Evo­lu­tion­ary Appli­ca­tions on June 6and Pro­ceed­ings of the Royal Soci­ety B on July 31, their research demon­strates that an intact for­est cor­ri­dor is vital for main­tain­ing gene flow in these great cats.

Human activ­ity in and around the Satpura-​Maikal for­est has dra­mat­i­cally changed the land­scape over the course of 300 years. From 1700 to 2000, the habi­tat under­went a 25-​fold increase in urban­i­sa­tion. Human pop­u­la­tion increased 10-​fold and anthro­pogenic activ­i­ties resulted in the clear­ing of 78 per­cent of the for­est, leav­ing just 32 per­cent of viable habi­tat for leop­ards and tigers. The reduced and frag­mented land­scape makes it dif­fi­cult for these soli­tary ani­mals to safely move between pro­tected reserved in search of mates and territory.

SCBI sci­en­tists col­lected 1,411 scat sam­ples, 66 hair sam­ples and four claw sam­ples and iden­ti­fied 217 leop­ards and 273 tigers in the same region. By extract­ing and analysing genetic mate­r­ial, sci­en­tists found that leop­ard gene flow between the four pro­tected areas in cen­tral India is much lower today than it has been in the past. The great­est decline of genetic diver­sity occurred between Mel­ghat and Pench, the two most frag­mented reserves. Reserves con­nected by for­est cor­ri­dors, how­ever, has a higher rate of gene flow, sug­gest­ing that habi­tat con­nec­tiv­ity directly affects the abil­ity of leop­ards to find an unre­lated mate.

Sci­en­tists found sim­i­lar results for tigers. Three of the reserve pairs with poor for­est con­nec­tiv­ity — Kanha-​Satpura, Pench-​Melghat and Kanha-​Melghat — showed a 47 to 70 per­cent reduc­tion in gene flow when com­pared to his­toric lev­els. The most dra­matic decrease in gene flow occurred between Kanha and Satpura-​Maikal, the pair of reserves with the least func­tional for­est corridors.

As part of these stud­ies, sci­en­tists recon­structed the demo­graphic his­tory of tigers in the Satpura-​Maikal land­scape. Using Bayesian and coalescent-​based analy­ses, sci­en­tists iden­ti­fied three points when tiger pop­u­la­tions clearly diverged. They found that tigers first entered India around 10,000 years ago. Their habi­tat frag­mented 700 years ago as agri­cul­tural expan­sion and other human activ­i­ties took place. In the 18th and 19th cen­turies, the third diver­gence event occurred as the British Empire expanded its ter­ri­tory and cleared the cen­tral Indian forests at an accel­er­ated rate. After this devel­op­ment, the tiger pop­u­la­tion was dras­ti­cally reduced and was fur­ther isolated.

As urban­i­sa­tion con­tin­ues to infringe upon the nat­ural Satpura-​Maikal land­scape, for­est cor­ri­dors play an increas­ingly impor­tant role in ensur­ing the sur­vival of leop­ard and tiger pop­u­la­tions. This research will be highly rel­e­vant to pol­icy mak­ers in cen­tral India as defor­esta­tion, road widen­ing and coal min­ing con­tinue to threaten tiger and leop­ard habi­tat. Both stud­ies call for the pro­tec­tion of cen­tral India’s for­est cor­ri­dors, which are vital to main­tain­ing genetic diver­sity in the pop­u­la­tions by main­tain­ing gene flow between pro­tected areas.

The above news item is reprinted from mate­ri­als avail­able at SI National Zoo­log­i­cal Park. Orig­i­nal text may be edited for con­tent and length.
(Source: SCBI Con­ser­va­tion Ecol­ogy Cen­ter news, 31.07.2013; Sci­ence­News news, 30.07.2013)

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